1. Field of the Invention
The present invention generally relates to a ball joint. More particularly, the invention relates to a ball joint that is suitable for use in an independent suspension for vehicles.
2. Description of Relevant Art
In general, as a joint for connecting two members to each other, universal joints, ball joints and the like are known.
Among such joints, ball joints are constituted in the form of a joint consisting of a ball shaft having a ball formed at the distal end thereof, the ball shaft being attached to one of two members to be interconnected with each other by the joint, and a ball housing accommodating the ball therein, the ball housing being attached to the other member.
Further, in recent years, in the field of suspensions for vehicles, particulary of independent suspensions, there have been provided ball joint type independent suspensions employing ball joints in place of king pins which had been ordinarily employed.
As an example of conventional ball joints in such ball joint type independent suspensions, there is shown in FIG. 5 a ball joint 100 of such a type that a ball housing and a ball are adapted to be rotatable relative to each other only about the axis of a ball shaft, to thereby achieve advantages in relation to the provision of sealing measures and endurability. The ball joint 100 employs a sealing structure including a dust boot 105 that is stretched between a member 103 at one side, to which a shaft portion 102 of a ball 101 is fixed, and a housing 104 attached to an unshown member at the other side, so as to cover the shaft portion 102. Incidentally, in FIG. 5, upward and downward directions thereof correspond to frontward and rearward directions of a vehicle (not shown).
The dust boot 105 is fixedly attached at the rear end (lower end in FIG. 5) thereof with a stop ring 108 embedded therein to the outer circumference of the front part of the housing 104, and has at the front end (upper end in FIG. 5) thereof a portion fitted along the inner circumference thereof on the shaft portion 102. In this front end portion is embedded an annular core member 107, while a frontwardly directed annular seal lip 106 is formed on such an outer circumferential pat of the front end portion of the dust boot 105 that faces the side of the member 103 to which the shaft portion 102 is fixed. Incidentally, in FIG. 5, designated at reference number 104a is a ball collar fitted tight so as to adapt the ball 101 to be rotatable, only about the axis of the shaft portion 102 thereof, with respect to the housing 104. Moreover, practically, the one side member 103 is a knuckle arm in a suspension, and the other side member that the housing 104 is attached to is an upper arm or a lower arm of the suspension.
By such arrangement of the ball joint 100 as described above, the one side member 103 that the shaft porton 102, as a ball shaft, is attached to is adapted to be rotatable, relative to the other side member that the housing 104 is attached to, about the axis of the ball shaft.
However, the seal lip 106 of the dust boot 105 is adapted to merely come into elastic contact with the one side member 103 due to the flexibility thereof. In this respect, since the ball joint 100 is disposed in the vicinity of a wheel in the suspension of the vehicle, the seal lip 106 is likely to catch dust or pebbles, thus raising a problem such that the sealability of the ball 101 may be reduced. Particularly, as the seal lip 106 is deteriorated with the time, such problem becomes remarkable, resulting in the possibility that a problem may arise in regard to the operability and/or endurability of the ball joint 100.
With such points in mind, the present invention has been achieved to effectively solve problems in conventional ball joints.